Khalid Masood: questions over how much MI5 knew about attacker

The prime minister disclosed that Masood was once investigated by MI5.When Theresa May mentioned MI5 in the Commons on Thursday, she was trying to be helpful, pre-empting criticism that the agency failed to prevent the London attack.As a tactic, it did not entirely work: Friday’s Daily Telegraph front page headline was “Killer escaped from MI5’s radar”.